To deal with challenges caused by the continuous scaling down of semiconductor devices, such as short channel effects, various high-performance devices, such as ultra-thin body and buried oxide (UTBB) and fin field effect transistor (FinFET) devices, are proposed.
The UTBB device utilizes an extremely thin semiconductor on insulator (ET-SOI) substrate. The SOI substrate can suppress the short channel effects due to a buried oxide (BOX) therein. Further, a back gate may be disposed on a back side of the SOI substrate, to control a threshold voltage of the device, and thus to reduce power consumption of the device (by, for example, enhancing the threshold voltage when the device is off and thus reducing current leakage). However, the ET-SOI substrate is significantly expensive and has problems such as self-heating. Further, the ET-SOI substrate is more and more difficult to manufacture with the trend of continuous scaling down.
The FinFET device is a 3D device, including a fin vertically formed on a substrate. A conductive channel may be formed in the fin. The fin may have its height increased while keeping its footprint unchanged, and thus may have an improved drive current per unit footprint. However, the FinFET device cannot effectively control its threshold voltage. Further, the fin becomes thinner and thinner with the trend of continuous scaling down, and tends to collapse during manufacture.